Color image copying with resolution control

ABSTRACT

A color image forming apparatus including: a discriminating circuit for discriminating a character portion of an object color image; a color image forming device for forming a color image and able to change the image-forming resolution; and a control circuit for causing change of the resolution of the color image forming device in accordance with the discrimination result provided by the discriminating circuit.

This application is a continuation of application No. 07/694,068 filedMay 1, 1991, now abandoned, which is a division of application Ser. No.07/367,673, filed Jun. 19, 1989, now U.S. Pat. No. 5,031,034.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing apparatus, and moreparticularly to optimum processing of a color image.

2. Related Background Art

Full-color images have been recently used extensively not only inprinting and design offices but also in general business offices. Inorder to read and output such color images with high fidelity, therehave been developed various types of color copying apparatus. Colorcopying apparatus are required to output a full-color image at highgradation, and also to output a color character document clearly and athigh resolution. As a method of outputting a full-color image at a highgradation, there are known a dither method, a screen dot modulationmethod and the like. If these methods are used for character images orline images, the resolution is considerably degraded and the quality ofcharacter is worsened. A binarization process is suitable for fairlyreproducing character images and line images. It is well known, however,that if the binarization process is used for screen dot images orphotographic images, the gradation and image quality are considerablydegraded. Various methods have been proposed to satisfy both characterquality and halftone quality. For example, (1) according to JapanesePatent Laid-Open Publication No. 61-11719, character quality is improvedby making black (BK) signal large and making yellow (Y), magenta (M) andcyan (C) signals small, based on the BK signal amplitude calculated fromcolor-separation Y, M and C signals, so that at the edge portion of ablack character, the respective color components are replaced with ablack component as much as possible; (2) there is also an attempt toimprove character quality by emphasizing all edges or contours of animage without degrading halftone; and (3) according to another method,high resolution image processing and high gradation image processing areselectively used by designating a character area, a screen dot area andphotographic area through manual input by an operator.

With the first method, the contour of a black character can berepresented by black color only. However, hairs or eyelashes aresometimes erroneously judged as a black character, or a superposition ofyellow, magenta and cyan screen dots is erroneously judged as a blackcharacter resulting in formation of an unnecessary black dot. Therefore,the first method is not satisfactory from the image quality viewpoint.With the second method, the sharpness of image is improved. However,since a black character portion is obtained by four-color superposition,color aberration occurs and the character quality is not satisfactory.With the third method, each image area can be processed independently.For example, the image area designated as a black character area isprocessed with high resolution using only black color, and the colorhalftone area is processed with excellent halftone. However, an operatoris required to precisely designate each image area position,necessitating very complicated operator work.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an image processingapparatus capable of solving the above-described problems independentlyfrom each other or at the same time.

It is another object of the present invention to provide an imageprocessing apparatus as above capable of adequately discriminatingbetween a character portion and a halftone portion of an object image.

It is a further object of the present invention to provide an imageprocessing apparatus capable of adequately discriminating particularly ablack character portion of an object image.

According to one preferred embodiment of this invention with the aboveobjects, an image processing apparatus is disclosed which comprisesfirst means for discriminating a black edge portion of an object image,second means for discriminating the color component near the edgeportion, and means for judging a characteristic of an object image inaccordance with the outputs from the first and second discriminatingmeans.

It is another object of the present invention to provide an imageforming apparatus capable of forming an object color image whileretaining a high resolution in the character portion or retaining a highgradation in halftone portion.

It is a further object of the present invention to provide an imageforming apparatus capable of properly forming an object color imagewithout color aberration in the black color portion.

According to another preferred embodiment of this invention, a colorimage forming apparatus is disclosed which comprises means fordiscriminating a character portion of an object color image; means forforming a color image with changeable resolution; and means forcontrolling change of the resolution of said color image forming meansin accordance with a discrimination result from said discriminatingmeans.

It is a still further object of the present invention to provide animage forming method suitable for use with thee color image formingapparatus as above. The other objects features and advantages of thepresent invention will become apparent from the following description ofthe preferred embodiments, taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of an image processingapparatus according to the present invention;

FIG. 2 shows the YIQ signal calculating circuit shown in FIG. 1;

FIG. 3 shows the achromatic color signal calculating circuit shown inFIG. 1;

FIG. 4 shows the black edge generating circuit shown in FIG. 1;

FIG. 5 shows the black level determining circuit shown in FIG. 1;

FIG. 6 shows the black character edge generating circuit shown in FIG.1;

FIG. 7 shows the image area signal generating circuit shown in FIG. 1;

FIG. 8 shows the black character correcting circuit shown in FIG. 1;

FIG. 9 shows the printer line number generating circuit shown in FIG. 8;

FIG. 10 is a block diagram showing a black character correcting circuit(for binarization process);

FIG. 11 is a block diagram showing a black character correcting circuit(for dither process);

FIG. 12 is a schematic diagram showing an example of a printer;

FIG. 13 shows the circuit arrangement of the triangle wave generatingmeans 208 shown in FIG. 12; and

FIG. 14 is a block diagram showing the circuit arrangement of anotherembodiment of the achromatic color signal calculating circuit shown inFIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An image processing apparatus suitable for copying a color image will bedescribed in connection with the following embodiments. However, it isto be noted that the invention is not intended to be limited thereto,but the invention is applicable to various apparatus.

1st Embodiment

FIG. 1 is a block diagram showing the circuit arrangement of the imageprocessing apparatus according to the first embodiment of thisinvention. Red (R), green (G) and blue (B) color signals for one pixelof a color document are read with a color document reader made of a CCD1 to which a mosaic filter is attached. In this embodiment, CCD 1outputs a dot sequential color signal which is amplified by an amplifier5 and color-separated into R, G and B signals at a color separationcircuit 7. A YIQ signal calculating circuit 10 calculates a luminancesignal Y and color signals I and Q. The luminance signal Y for obtaininga black character edge signal is inverted into a black edge signal Y andsupplied to a black edge quantity generating circuit 40 whereat a blackedge quantity signal KE is outputted by deriving an edge thereof througha Laplacian operator operator. The I and Q signals representative of acolor difference from an achromatic color are inputted to an achromaticcolor signal calculating circuit 20 which outputs an achromatic colorsignal W by using a lookup table. The larger the value of W signalbecomes, the closer the color is being achromatic. The W and Y signalsare inputted to a black level determining circuit 50 whereat the levelof a dark achromatic color, i.e., a black, is outputted as a T signal ofbinary value. A black character edge generating circuit 60 receives theblack edge quantity signal KE and generates black character edge signalsE1 and E2, in accordance with the black level signal. The E1 signal isused for emphasizing the edge of a black character, and the E2 signal isused for removing color aberration at the black color edge. An imagearea signal generating circuit 70 judges as an image area (i.e., not acharacter area) any area having a bright chromatic color and includingits vicinity, and outputs an image area determining signal Z. A blackcharacter correcting circuit 80 obtains cyan (C), magenta (M), yellow(e) and black (K) signals based on the R, G and B signals. Next, thefollowing correction is conducted for those signals in the area withrespect to which the image area signal Z is not outputted and the blackcharacter edge signals E1 and E2 are outputted. The C, M and Ye signalsare each added with E2, and the K signal is added with E1, respectivelyas their correction signal. The resultant signals are outputted to thenext stage output apparatus such as a printer. P represents a printerline number signal which indicates a resolution.

Next, the details of the circuits shown in FIG. 1 will be given.

The YIQ signal calculating circuit 10 for receiving R, G and B signalsand outputting Y, I and Q signals shown in FIG. 1 will be described withreference to FIG. 2. In FIG. 2, multipliers 11, 12 and 13 each multiplythe R, G and B signal by a parameter aij (where i, j=1, 2, 3) which isstored in a memory 14. A selector 15 selects the parameters and setsthem at the respective multipliers 11, 12 and 13. An adder 16 addstogether the outputs of the multipliers 11, 12 and 13. A selector 17selectively outputs Y, I and Q signals based on the output from theadder 16. The signal Y is represented by a11 x R+a12 x G +a13 x B, thesignal I is represented by a21 x R+a22 x G+a23 x B, and the signal Q isrepresented by a31 x R+a32 x G+a33 x B.

The selector 15 sequentially selects three sets of parameters (a11, a12,a13), (a21, a22, a23) and (a31, a32, a33), respectively for the inputtedR, G and B signals of one pixel. Therefore, the adder 16 sequentiallyoutputs Y, I and Q signals, respectively for the inputted R, G and Bsignals of one pixel. The selector 117 selects the sequentially inputtedY, I and Q signals and outputs them onto lines a, b and c, respectively.

The details of the achromatic color signal calculating circuit 20 willbe described with reference to FIG. 3. A multiplier 21 outputs a squareof I, and a multiplier 22 outputs a square of Q. An adder 23 addstogether the outputs of the multipliers 21 and 22, and outputs (I² +Q²).A lookup table 24 outputs a signal W based on the inputted (I² +Q²). Theoutput W is determined by the following equation: ##EQU1##

The above-described inverter 30 inverts the signal Y into a signal Y.

The detail of the black edge quantity generating circuit 40 will bedescribed with reference to FIG. 4. Line buffers 31, 32, 33, 34 and 35are provided for an object pixel and associated peripheral pixels. Aprocessing circuit 36 calculates an edge quantity in the followingmanner. An object pixel x33 is represented by Y, where xij (i, j=1, 2,3, 4, 5) represents the value stored in the line buffer. The edgequantity is obtained by the following equation:

    KE=X.sub.33 -(X.sub.11 +X.sub.15 +X.sub.51 +X.sub.55)/4

The detail of the black level determining circuit 50 will be describedwith reference to FIG. 5. A multiplier 51 multiplies Y by W. The outputu of the multiplier 51 is supplied to a threshold processing circuit 52which outputs, as a black level signal T, 0 for u<T0, 1 for T0≦u<T1, 2for T1<u<T2, and 3 for T2≦u.

The above-described edge signal calculating circuit 60 outputs two edgesignals E1 and E2 based on the black edge quantity signal KE from theblack edge quantity generating circuit 40 and the black level signal Tfrom the black level determining circuit 50. The detail of the edgesignal calculating circuit 60 will be described with reference to FIG.6. A comparator 61 compares the signal KE with a threshold value storedin a memory 62, and outputs 1 if the signal KE is larger than thethreshold value, and outputs 0 if not. A processing circuit 63calculates the edge signal E1 based on the KE and T signals and anoutput of the comparator 61. The processing circuit 63 outputs thesignal E1=0 if the output of the comparator 61 is 0, and the signalE1=α₁ ×KE if the output of the comparator 61 is 1. The constant α₁ isoptionally determined in accordance with the value of the signal T. Acomparator 64 compares the signal KE with a threshold value stored in amemory 65, and outputs 1 if the signal KE is larger than the thresholdvalue, and outputs 0 if not. A processing circuit 66 calculates the edgesignal E2 based on the KE and T signals and an output of the comparator64. The threshold value of 0 is stored in the memory 65. The processingcircuit 66 outputs the signal E2=KE×(-1)×α₂ if the output of thecomparator 64 is 0 , and the signal E2=KE ×α₂ if the output of thecomparator 64 is 1. The constant is optionally determined in accordancewith the value of the signal T.

The detail of the image area determining circuit 70 will be describedwith reference to FIG. 7. A multiplier 71 multiplies the signal Y by thesignal W obtained by inverting the signal W, and outputs a signal X. Athreshold processing circuit 72 compares and predetermined thresholdwith the X signal and outputs the comparison result. Line buffers 73, 74and 75 store the outputs of the threshold processing circuit 72. Adetermining signal generating circuit 76 reads the values of the objectpixel and associated pixels from the line buffers 73, 74 and 75, anddetermines if the object pixel is within an image area or not. If theobject pixel is within the image area, the circuit 76 outputs 1 as theimage area signal Z, and outputs 0 if not.

The detail of the black character correcting circuit 80 will bedescribed with reference to FIG. 8. A CMYK calculating circuit 81calculates cyan (Co), magenta (Mo), yellow (Yo) and black (Ko) signalsbased on the R, G and B signals by using a known technique. The CMYKcalculating circuit 81 includes therein a circuit for converting R, Gand B signals into Ye, M and C signals, a color masking circuit, and acircuit for performing a UCR process and outputting the black (Bo)signal. An AND gate 82 receives the black level signal T and image areadetermining signal Z, and outputs 1 if the black level signal is not 0and the image area determining signal is 0, and outputs 0 in the othercases. A selector 83 outputs E1'=E1 and E2'=E2 if the output of the gate82 is 1, and outputs E1'=0 and E2'=0 if the output of the gate 82 is 0.An adder 84 adds together the signal Co and signal E2', an adder 85 addstogether the signal Mo and signal E2', an adder 8 adds together thesignal Yo and signal E2', and an adder 87 adds together the signal Koand signal E1'. A printer line number signal generating circuit 88receives the E1' signal and outputs a printer line number signal P byprocessing the pixels adjacent the object pixel, the signal Prepresenting a printer output resolution. FIG. 9 shows the detail of theprinter line number signal generating circuit 88. A comparator 881outputs 0 if the E1' signal is 0, and outputs 1 if not. The output 0stands for a low resolution output, and the output 1 for a highresolution output. Line buffers 882, 883 and 884 store the output of thecomparator 881 for the object pixel and associated pixels, e.g., 5×5pixels. An OR gate 885 outputs 1 indicating that the object pixel isoutputted at a high resolution, if any one of the object pixel andassociated pixels shows a high resolution output, and in the other case,the OR gate 885 outputs 0. With the above circuit arrangement, it ispossible to prevent frequent change of the output of the printer linenumber signal generating circuit, which will be described later.

Shown in FIG. 12 is an example of the image forming apparatus (laserprinter) for forming an image by using an image signal outputted fromthe above-described image processing apparatus. In the embodimentapparatus shown in FIG. 12, the gradation is reproduced by means of amethod called PWM modulation. A latch section 201 latches a digitalvideo signal in synchronism with a clock VK obtained byfrequency-dividing master clocks at a J/K flip-flop (J/K-FF) 205. A D/Aconverter 202 converts the latched digital video signal into an analogsignal. A dynamic range adjustment means 225 adjusts the dynamic rangeof an output of the D/A converter. A flip-flop 206 controls the phase ofthe master clock. Reference numeral 222 represents a CPU. A flip-flop213 frequency-divides the clocks whose phase was controlled by theflip-flop 206. A triangle wave generating means 208 outputs a trianglewave to serve as what is sometimes referred to herein as a patternsignal, in accordance with an output from the flip-flop 213. Acomparator 204 compares the output of the dynamic range adjustment means225 with the output of the triangle wave generating means 208 whichincludes bias adjustment means 224 for adjusting the bias of thetriangle wave. In this embodiment, the triangle wave generating meanscan selectively output a first triangle wave of relatively highfrequency and a second triangle wave having a lower frequency than thatof the first triangle wave. Such selection is controlled in accordancewith an output from CPU 222 which also controls the other circuits ofthe apparatus. A ROM 226 stores therein operation programs. A RAM 227 isused as a working area of CPU 222.

Reference numeral 229 represents a drum type electronic photosensitivemember rotating in the direction indicated by an arrow. Thephotosensitive member 229 is uniformly charged by a charger 230. Next, alaser beam 231 modulated to output radiation in response to a modulationsignal E outputted from the comparator 204 scans and exposes thephotosensitive member 229 in the direction generally perpendicular tothe direction of rotation of the photosensitive member 229. Anelectrostatic latent image formed on the photosensitive emmber 229 isvisualized by a developer 232.

A visualized toner image is transferred on a transfer sheet 234 by meansof a transfer charger 233. The transferred image on the transfer sheet234 is fixed by a fixer (not shown), whereas the remaining toner on thephotoconductive member 229 is removed by a cleaner 235. Thereafter,electric charge left on the photosensitive member 229 is removed uponapplication of light from a lamp 236. The above processes are repeatedthereafter.

In this embodiment, Ye, M, C and K toners are prepared toframe-sequentially print four colors, i.e., to form a full-color image.

The laser beam 231 is emitted from a semiconductor laser 237 which isdriven by a driving circuit 241 to which a pulse-width-modulation signalA outputted from the comparator 204 is applied. Therefore, emitted fromthe semiconductor laser 237 is a laser beam 231 which is modulated tooperate in response to the modulation signal E.

The laser beam 231 emitted out from the semiconductor laser 237 isscanned by means of a scanner 238 such as a rotary polygon mirror,galvano mirror or the like. A lens 239 focuses the laser beam 231 ontothe photosensitive member 229. A mirror 240 is used to reflect the laserbeam 231.

FIG. 13 shows another example of the triangle wave generating means 208and its peripheral circuits shown in FIG. 12, wherein an image is formedthrough pulse width modulation. A digital video signal Vin from aninterface is latched at a latch in synchro with a video clock VCLK. Thedigital video signal Vin is then converted into an analog video signalAV at a D/A converter 302. An output of the D/A converter 302 is leveladjusted by a resistor 303 and supplied to one terminal of twocomparators 304a and 304b. In this embodiment, two triangle wavegenerating means are provided, each being made of an integrationcircuit. The two triangle wave generating means integrate the outputs ofJ/K flip-flops 305 and 313 which halve different clocks PHCLK and TXCLKin response to the clock VCLK. The frequency of TXCLK is set at arelatively high frequency for the purpose of high resolution use, e.g.,400 dpi, whereas the frequency of PHCLK is set at a relatively lowfrequency for the purpose of high gradation, e.g., 200 dpi. Thesefrequency divided clocks having a 50% duty ratio are supplied to buffers306a and 306b and then to integration circuits constructed of resistors307a and 307b and capacitors 308a and 308b, to thereby generate trianglewaves whose biases are adjusted by capacitors 309a and 309b andresistors 310a and 310b. The triangle waves are supplied to the otherterminals of the comparators 304a and 304b and compared with the analogvideo signal AV to thus generate two pulse width modulation signals Eaand Eb.

The two signals Ea and Eb are inputted to a switch 318. A selector 318selects, in accordance with a control signal CIS from a CPU 322, thesignal Ea for a character area or the signal Eb for a photograph area(halftone image). Such selection is conducted by CPU 322 operating insynchro with a signal corresponding to the signal P shown in FIG. 1. Aselection circuit 354 selects, in accordance with a select signal,either an output from a counter 352 or an address outputted from CPU viaan address bus. A circuit 358 outputs a signal to a D-type flip-flop 350in accordance with the address outputted from the selector and the dataoutputted from CPU via a data bus.

CPU 322 sets an address and data at the selectors 354 and 358 whichselect one of the outputs of the comparators 304a and 304b, inaccordance with the signal P outputted from the black charactercorrecting circuit 80 shown in FIG. 1.

With the circuit arrangement shown in FIG. 13, CPU can perform a desiredcorrection by selecting one of the outputs from the comparators 304a and304b in accordance with an output from the black character correctingcircuit 80.

In the embodiment shown in FIG. 12, the frequency of the triangle waveoutputted from the triangle wave generating means and inputted to thecomparator 204 has been changed. However, in the embodiment shown inFIG. 13, two comparators 304a and 304b are provided to select one of theoutputs, thereby improving the circuit response.

According to the above-described image forming apparatus, an edge isemphasized for an area judged as a character area, whereas an edge isnot emphasized for an area judged as a screen dot color image area. Inaddition, a frequency a is automatically selected for the purpose ofhigh resolution use for an area judged as a character area, and afrequency b for the purpose of high gradation for an area judged as acolor image area. Consequently, the quality of a reproduced image can befurther improved.

2nd Embodiment

The second embodiment of the black character correcting circuit shown inFIG. 1 will be described, wherein a black character processing isperformed for an area near a derived character image and line image areahaving an optional color.

FIG. 10 shows the black character correcting circuit using abinarization process. A circuit 91 calculates cyan (Co), magenta (Mo),yellow (Yo) and black (Ko) signals based on the R, G and B signals byusing a known technique. An AND gate 92 outputs 1 if the black levelsignal T takes a value other than 1 and the image area signal takes avalue 0, and outputs 0 in the other cases. A printer line numberdetermining circuit 93 determines the number of printer lines based onthe output of the AND gate 92 for the object pixel and associatedpixels. Selectors 94, 95, 96 and 97 output 0, 0, 0 and Ko respectivelyif the printer line number signal P is 1, and output Co, Mo, Yo and 0respectively if the signal P is 0.

3rd Embodiment

The third embodiment of the black character correcting circuit shown inFIG. 1 will be described, wherein a black character processing isperformed for an area near a derived character image and line image areahaving an optional color.

FIG. 11 shows the black character correcting circuit using abinarization process. A circuit 101 calculates cyan (Co), magenta (Mo),yellow (Yo) and black (Ko) signals based on the R, G and B signals byusing a known technique. An AND gate 102 outputs 1 if the black levelsignal T takes a value other than 1 and the image area signal takes avalue 0, and outputs 0 in the other cases. A printer line numberdetermining circuit 103 determines the number of printer lines based onthe output of the AND gate 102 for the object pixel and associatedpixels. A dither processing circuit 104 performs a known dither processif only the output of the printer line number generating circuit 103 is0, and it passes the inputted signal without processing it if the outputof the circuit 103 is 1.

In the above embodiments, a black area is first derived in accordancewith the brightness information and chrominance information of adocument, and then an edge component of the document is derived tothereby judge the black edge portion. A black character, color image andblack fine line within the screen dots are automatically discriminatedin accordance with the degree of the black edge and the degree of colorinformation of adjacent pixels. Therefore, without labor of an operator,both a high quality halftone or dots and a high quality black charactercan be realized.

Specifically, according to the embodiments, in discriminating thecharacteristic of an object image, not only the high frequency and colorcomponents of the object image but also the color components of theadjacent area are detected so that there is no fear of erroneouslyjudging as a black character the black dot area where respective colorscreen dots are superposed one upon another within a color image made ofscreen dots. Therefore, a character having an optional color can bediscriminated from other image areas such as color image area made ofscreen dots. It is accordingly possible to suppress color aberration ofa black character, reduce the number of erroneous judgements thatsuperposed respective color dots within a color screen dot image areconsidered as a black character, and improve the quality of a blackcharacter considerably. Further, both the characters and color imagewithin one document can be automatically discriminated.

4th Embodiment

In the above-described embodiments, a black character is derived from animage. If a red character is to be derived, as the value of theluminance signal Y, the value of the R signal is outputted from the YIQcalculating circuit. In the above embodiments, the Y signal is obtainedusing the equation Y=a11 x R+a12 x G+a13 x B. In this embodiment, thevalues of parameters are set as a11=1, a12=0 and a13=0.

The lookup table has been described for obtaining I, Q and W signals atthe achromatic color signal calculating circuit. However, the followingequation may be used:

    W=255*exp[-(16/255).sup.2 ·{(I-a).sup.2 +(Q-b).sup.2 }]

wherein a and b are a constant. Other parameters may be used if a signalrepresenting the degree of chromaticity and achromaticity is used.

Another embodiment of the achromatic color signal calculating circuitshown in FIG. 3 will be described with reference to FIG. 14. In FIG. 14,a maximum value calculating circuit 191 detects a maximum value among R,G and B signals, and a minimum value calculating circuit 192 detects aminimum value among R, G and B signals. A subtracter 193 subtracts theminimum value from the minimum value calculating circuit 192, from themaximum value from the maximum value calculating circuit 191. Aninverter 194 inverts the output from the subtracter 193 and outputs anachromatic color signal W.

The degree of achromaticity may be judged by various other methods inplace of the embodiment method.

In the above embodiment, as a method of detecting a high frequencycomponent of an object image, an edge within the object image has beendiscriminated. However, the invention is not limited thereto, but acircuit which simply derives the high frequency component from imageinformation may also be used.

As described so far, according to the embodiments, a character area andother image areas can be discriminated. It is accordingly possible tosuppress color aberration of a black character, reduce the number oferroneous judgments that superposed respective color dots within a colorscreen dot image are considered as a black character, and improve thequality of a black character considerably. Further, without labor of anoperator, both a character and a color image can be automaticallydiscriminated to thereby provide good operation efficiency.

In the above embodiments, the image area determining circuit shown inFIGS. 1 and 7 has been used as the means for discriminating the colorcomponent near an edge. However, the invention is not limited thereto,but other arrangements may be used. For example, another dedicatedsensor may be used in addition to CCD 1.

As appreciated from the foregoing description of the embodiments, acharacter image, line image and color image can be discriminated at highprecision and reliability.

What is claimed is:
 1. A color image copying apparatuscomprising:reading means for reading an original image and foroutputting a plurality of color component signals; first means fordiscriminating an edge portion of the original image; second means fordiscriminating a plurality of color components near the edge portion;means for judging a characteristic of the original image in accordancewith outputs from said first and second discriminating means; and meansfor forming a color image, said color image forming means being able tochange resolution in accordance with a result output by said judgingmeans.
 2. An apparatus according to claim 1, wherein said reading meansfurther comprises a color filter and a photosensor.
 3. An apparatusaccording to claim 1, wherein said first means further comprises delaymeans for delaying the plurality of color component signals, and meansfor processing the plurality of color component signals delayed by saiddelaying means and the plurality of color component signals not yetdelayed by said delaying means.
 4. A color image processing methodcomprising the steps of:discriminating a black character portion from agiven color image signal; emphasizing black and changing a resolution ofa color image forming device with regard to the discriminated blackcharacter portion; and supplying the color image signal processed insaid emphasizing step to the color image forming device, wherein saidresolution is changed to first resolution suitable for an image formingof a portion which is not the black character portion and a secondresolution suitable for an image forming of a portion which is the blackcharacter portion, said second resolution being higher than the firstresolution.
 5. A method according to claim 4, wherein said emphasizingstep comprises black monocolor processing.
 6. A method according toclaim 4, wherein the resolution of the color image forming device isvariable, and further comprising the step of processing the color imagesignal to vary the resolution of the image to be formed.
 7. A methodaccording to claim 4, further comprising the step of reading an originalto generate the color image signal.
 8. A method according to claim 4,wherein the black character portion discriminated in said discriminatingstep is a portion at an edge portion and having a high black level.
 9. Acolor image copying method comprising the steps of:reading an originalimage; outputting a plurality of color component signals; discriminatingan edge portion of the original image; discriminating a plurality ofcolor components near the edge portion; judging a characteristic of theoriginal image in accordance with the discriminations of the edgeportion and of the plurality of color components near the edge portion;forming a color image, wherein resolution is changed in accordance witha result of the judging step.
 10. A color image copying method accordingto claim 9, wherein the step of reading further comprises using a colorfilter and a photosensor.
 11. A color image copying method according toclaim 9, wherein the step of discriminating the edge portion furthercomprises a step of delaying the plurality of color component signals,and processing the plurality of color component signals delayed in thedelaying step and the plurality of color component signals not yetdelayed in the delaying step.